The full length fuel rods (FLFRs in the following specification) are received between the base and the head of the fuel assembly with a small longitudinal gap allowing the FLFRs to expand in their longitudinal direction during operation of the nuclear reactor.
Usually, the upper ends of the FLFRs are attached to the nuclear fuel assembly head.
The partial length fuel rods (PLFRs in the following specification) are used in boiling water reactors (BWR in the following specification) for reasons of thermo-hydraulic stability and neutron moderation.
PLFRs extend upwardly from the fuel assembly base and stop at a distance from the fuel assembly head. Usually, the PLFRs length is comprised between 25% and 75% of the FLFRs length.
The fuel rods are positioned and held longitudinally and transversally by a plurality of spacer grids spaced along the fuel rods. These spacer grids allow for local and limited sliding movement of the fuel rods in the spacer grids to accommodate the fuel rod expansion under irradiation.
Nevertheless, under specific operating conditions, the longitudinal holding force applied by the spacer grids to the bundle of fuel rods may be not sufficient to avoid any longitudinal global displacements of some of the rods.
Accordingly, in order to prevent the PLFRs from lifting-off during the nuclear reactor operation and reaching undesired positions, PLFRs are usually attached to the fuel assembly base.
DE-201 05 913 discloses a fuel assembly where such an attachment is made, for each PLFR, through an elastic bushing welded in a through hole provided in the base of the fuel assembly.
However, such a design requires the welding of additional parts to the nuclear fuel assembly base and is therefore complicated and expensive to manufacture.
US-2008/101528 teaches a simpler and cheaper arrangement. In this arrangement, which corresponds to the preamble of claim 1, the lower ends of the PLFRs are attached to the nuclear fuel assembly base through clips integral with the base and forming the housings. However, such an arrangement still requires specific machining to achieve adequate tolerances for the clips. Therefore, while such an arrangement is satisfactory, it is still desirable to simplify its design and lower its price.